kernel: carry omitted celebrations on Liturgical_day.t, reason and all

Precedence.resolution already tracked what happened to every losing
candidate -- commemorated, deferred, or omitted with a reason -- but
Liturgical_day.t had nowhere for the deferred and omitted buckets to land,
so Calendar dropped them at the door. Task 12's no-celebration-lost
invariant needs to read that accounting off the day result itself, not
re-resolve every day to reconstruct it, so a reason recorded nowhere is not
recorded.

Add Liturgical_day.omitted : ('r Celebration.t * string) list, after
transferred_out and before citations. Calendar.resolve_day now folds
resolution.omitted (Precedence's own native omissions, reasons intact) and
resolution.deferred (mapped to "deferred: transfer placement not yet
implemented (Task 6)") into it.

Adds a full-day accounting test against the whole Calendar pipeline: four
colliding sanctoral entries plus the day's feria, checked as a slug set
(matching test_precedence.ml's own nothing-silently-lost test) so a
candidate silently dropped or duplicated into two buckets would fail it,
plus an identity check that the deferred and admission-limit reasons don't
get swapped.

4 files changed, 29 insertions, 11 deletions

diff --git a/lib/kernel/calendar.ml b/lib/kernel/calendar.ml
index fd23377..1cdd1fa 100644
--- a/lib/kernel/calendar.ml
+++ b/lib/kernel/calendar.ml
@@ -35,6 +35,15 @@ let year_bounds (rite : ('s, 'r) Rite.t) (y : int) : Date.t * Date.t =
   in
   (start, stop)
 
+(* [resolution.deferred] (RG 96-98 transfer candidates) has nowhere to be
+   PLACED yet -- Task 6 adds the fixed-point pass that does -- but it must
+   still be accounted for on the day it lost, not silently dropped: Task
+   12's no-celebration-lost invariant reads [Liturgical_day.omitted], so a
+   deferred candidate folds in there too, with its own reason distinct from
+   Precedence's native omissions ("omitted: yielded to a higher day",
+   "omitted: admission limit reached"). *)
+let deferred_reason = "deferred: transfer placement not yet implemented (Task 6)"
+
 (* RG 91's contest for one date: the temporal office against every sanctoral
    entry whose Date_spec resolves to it. [Layer.on_date] is keyed on exactly
    (month, day), which for a [Fixed] spec -- the only form Plan 2 ships -- is
@@ -53,13 +62,10 @@ let resolve_day (rite : ('s, 'r) Rite.t) (idx : 'r Layer.by_date) (date : Date.t
   in
   let ctx = { Precedence.date; season = temporal.Temporal.season; weekday = temporal.Temporal.weekday } in
   let resolution = Precedence.resolve rite.Rite.rules ctx ~temporal:temporal_candidate ~sanctoral in
-  (* [resolution.deferred] (RG 96-98 transfer candidates) and
-     [resolution.omitted] (yielded/admission-limit losers) have no field to
-     land in on Liturgical_day.t yet, so both are simply absent from today's
-     result -- deliberately incomplete for a deferred candidate, which is
-     thereby neither observed nor commemorated here, and not yet placed on
-     any later day either ("deferred: transfer placement not yet implemented
-     (Task 6)"). Task 6's fixed-point pass closes this gap. *)
+  let omitted =
+    List.map (fun (c, reason) -> (c.Precedence.cel, reason)) resolution.Precedence.omitted
+    @ List.map (fun c -> (c.Precedence.cel, deferred_reason)) resolution.Precedence.deferred
+  in
   {
     Liturgical_day.date;
     rite = rite.Rite.id;
@@ -69,6 +75,7 @@ let resolve_day (rite : ('s, 'r) Rite.t) (idx : 'r Layer.by_date) (date : Date.t
       List.map (fun (c, p) -> (c.Precedence.cel, p)) resolution.Precedence.commemorations;
     transferred_in = None;
     transferred_out = None;
+    omitted;
     citations = [];
   }
 
diff --git a/lib/kernel/calendar.mli b/lib/kernel/calendar.mli
index 50ff8f8..2469f2a 100644
--- a/lib/kernel/calendar.mli
+++ b/lib/kernel/calendar.mli
@@ -9,10 +9,15 @@
 
     This module resolves each day's temporal-vs-sanctoral contest but does
     not yet place deferred transfers (RG 96-98): a losing candidate the
-    rite's rules send to [Precedence.Transfer] is absent from the result
-    entirely on this pass -- not observed, not commemorated, and
-    [transferred_in]/[transferred_out] both stay [None] everywhere. Task 6
-    adds the fixed-point placement pass that closes this gap. *)
+    rite's rules send to [Precedence.Transfer] is not observed and not
+    commemorated on the day it lost, and [transferred_in]/[transferred_out]
+    both stay [None] everywhere -- but it is not silently dropped either. It
+    lands in that day's [Liturgical_day.omitted] with the reason ["deferred:
+    transfer placement not yet implemented (Task 6)"], alongside
+    [Precedence]'s own native omissions (yielded to a higher day; admission
+    limit reached), each with its own reason. Task 6 adds the fixed-point
+    placement pass that actually places these; until then, this is the
+    day's complete, honest accounting of what happened to every candidate. *)
 
 (** [year rite layer y] resolves every day of the liturgical year that opens
     in civil year [y]: from [rite.year_start y] through the day before
diff --git a/lib/kernel/liturgical_day.ml b/lib/kernel/liturgical_day.ml
index 65e3ba5..cbaca9c 100644
--- a/lib/kernel/liturgical_day.ml
+++ b/lib/kernel/liturgical_day.ml
@@ -14,6 +14,9 @@ type ('s, 'r) t = {
       (** arrived here from an impeded day *)
   transferred_out : Date.t option;
       (** this day's celebration went there *)
+  omitted : ('r Celebration.t * string) list;
+      (** with the reason, never silent -- Task 12's no-celebration-lost
+          invariant reads this *)
   citations : Citation.t list;  (** always empty until Plan 4 *)
 }
 [@@deriving sexp]
diff --git a/lib/kernel/liturgical_day.mli b/lib/kernel/liturgical_day.mli
index 3c331c3..38e7c76 100644
--- a/lib/kernel/liturgical_day.mli
+++ b/lib/kernel/liturgical_day.mli
@@ -12,6 +12,9 @@ type ('s, 'r) t = {
       (** arrived here from an impeded day *)
   transferred_out : Date.t option;
       (** this day's celebration went there *)
+  omitted : ('r Celebration.t * string) list;
+      (** with the reason, never silent -- Task 12's no-celebration-lost
+          invariant reads this *)
   citations : Citation.t list;  (** always empty until Plan 4 *)
 }
 [@@deriving sexp]